With current widespread use of large-screen terminals such as mobile terminals, touch panel-type mobile terminals, and tablet terminals, pressure-sensitive adhesive sheets for protecting the surface of large screens (surface protective sheets) have come to be used. However, there is a problem in that air bubbles can be trapped by a pressure-sensitive adhesive sheet being attached to the surface of a large screen, and the pressure-sensitive adhesive (layer) of the pressure-sensitive adhesive sheet is required to have high wetting ability on the adherend.
When no longer needed, the attached pressure-sensitive adhesive sheet will be peeled off and removed. Therefore, the pressure-sensitive adhesive sheet is required to be lightly peelable for improved peeling workability.
Conventional pressure-sensitive adhesive sheets with high wetting ability and light peelability are produced using silicone-based pressure-sensitive adhesives. However, silicone-based pressure-sensitive adhesives are expensive and less economical and may cause staining with the silicone itself, which means that they are unsuitable for use in fields where staining can cause a serious problem, such as a process of manufacturing electronic components or the like.
On the other hand, the use of acrylic pressure-sensitive adhesives is disclosed (Patent Documents 1 to 3), which can be an alternative to the use of silicone-based pressure-sensitive adhesives. Unfortunately, acryl-based polymers in acrylic pressure-sensitive adhesives have the following problem. Acryl-based polymers have a C—C—C bond as a main component of the polymer skeleton and therefore have a structure in which free rotation of the bond in the polymer chain is restricted, so that the motion of the polymer molecule is restricted. Therefore, acrylic pressure-sensitive adhesives are less likely to have good wetting ability.